In a liquid crystal display panel including an active matrix substrate, a thin film transistor (hereinafter referred to as a “TFT”) is provided in each pixel, which is the smallest unit of an image, for example. By switching each TFT on or off to reliably apply a predetermined voltage to the liquid crystal layer of the corresponding pixel, a high-resolution image can be displayed.
In recent years, as the pixel resolutions of active matrix substrates and liquid crystal display panels including the active matrix substrates have been increased, there has been a higher risk of a defect occurring in a pixel, which is, for example, caused when film formation or etching is performed in the presence of foreign matter (called a particle) adhering to a substrate surface during manufacture of the active matrix substrate.
For example, PATENT DOCUMENT 1 describes a testing method for finding a short-circuit defect between a scanning line and a signal line which include a plurality of interconnects by passing a current between the scanning line and the signal line, and particularly, for identifying the address of a defective pixel using an infrared image.
PATENT DOCUMENT 2 describes a testing method and device for identifying the address of a defective pixel using an infrared image, particularly by causing the power supply and the substrate load impedance to match each other so that power transmission is maximized, thereby increasing heating efficiency, and utilizing a difference in relaxation time of a transient phenomenon of temperature increase between a defective pixel and a normal pixel.
In the defect detection methods of PATENT DOCUMENTS 1 and 2, however, the infrared imaging device is directed to the entire display panel, and therefore, a defective pixel can be identified, but the position of a defective portion in the defective pixel may not be accurately identified.